linux-kernel - Re: [PATCH v6 0/2] KVM: MMU: fix kvm_is_mmio

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Date:   Wed, 20 Dec 2017 11:12:52 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Haozhong Zhang <haozhong.zhang@...el.com>, kvm@...r.kernel.org,
        x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, rkrcmar@...hat.com,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Dan Williams <dan.j.williams@...el.com>,
        ivan.d.cuevas.escareno@...el.com, karthik.kumar@...el.com,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Olif Chapman <olif.chapman@...cle.com>,
        Mikulas Patocka <mpatocka@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH v6 0/2] KVM: MMU: fix kvm_is_mmio_pfn()

On 20/12/2017 08:29, Haozhong Zhang wrote:
> Some reserved pages, such as those from NVDIMM DAX devices, are not
> for MMIO, and can be mapped with cached memory type for better
> performance. However, the above check misconceives those pages as
> MMIO.  Because KVM maps MMIO pages with UC memory type, the
> performance of guest accesses to those pages would be harmed.
> Therefore, we check the host memory type in addition and only treat
> UC/UC-/WC pages as MMIO.
> 
> Changes in v6:
>  * Rename the function in patch 1 to pat_immune_to_uc_mtrr().
>  * Consider WC memory type in patch 1.
> 
> Changes in v5:
>  * Rename pat_pfn_is_uc() into pat_pfn_is_uc_or_uc_minus() to avoid
>    confusion.
>  * Drop converters between kvm_pfn_t and pfn_t, because they are not
>    necessary. pat_pfn_is_uc_or_uc_minus() does not need flags in
>    pfn_t, so we can only pass a raw unsigned long to it.
> 
> Changes in v4:
>  * Mask pfn_t and kvm_pfn_t specific flags in conversion.
> 
> Changes in v3:
>  * Move cache mode check to pat.c as pat_pfn_is_uc()
>  * Reintroduce converters between kvm_pfn_t and pfn_t.
> 
> Changes in v2:
>  * Switch to lookup_memtype() to get host memory type.
>  * Rewrite the comment in KVM MMU patch.
>  * Remove v1 patch 2, which is not necessary in v2.
> 
> Haozhong Zhang (2):
>   x86/mm: add a function to check if a pfn is UC/UC-/WC
>   KVM: MMU: consider host cache mode in MMIO page check
> 
>  arch/x86/include/asm/pat.h |  2 ++
>  arch/x86/kvm/mmu.c         | 13 ++++++++++++-
>  arch/x86/mm/pat.c          | 19 +++++++++++++++++++
>  3 files changed, 33 insertions(+), 1 deletion(-)
> 

Thanks, I applied this series.  I only changed the function name to
pat_pfn_immune_to_uc_mtrr.

Thanks,

Paolo